The present invention relates to an internal combustion engine with dual induction system including a primary induction system to direct a first fluid charge into a cylinder to swirl therein under all operating conditions of the engine and a secondary inductionsystem to direct a second fluid charge into the cylinder in such a direction as to impede and reduce the swirling motion of the first fluid charge issuing from the primary induction system under predetermined operating conditions of the engine, thereby maintaining the volumetric efficiency of the engine at sufficiently high level. More particularly, the invention relates to an exhaust gas recirculation (EGR) system for an internal combustion engine as above.
For facilitating evaporation of fuel droplets and increasing flame propagation, it is known to cause an air fuel mixture charge to swirl around the cylinder axis. With this, more stable combustion at low and intermediate loads has resulted. For this purpose various fuel mixture introductions have been employed to produce fuel mixture swirling around the cylinder axis, for example complicated intake port shapes; or shrouded intake valves. If such a complicated induction arrangement is employed, the volumetric efficiency of the engine suffers at high loads and as a result the power output under full or high load conditions drops.
In order to reduce a drop in the volumetric efficiency of the engine, an internal combustion engine with dual induction system is known. In operation of the engine, at low and intermediate loads an air fuel mixture is drawn from a primary induction system only into a cylinder to swirl around the cylinder axis, and at high loads, a secondary induction system becomes operative to direct an air fuel mixture or air into the cylinder in such a direction as to impede and reduce the swirling motion of the mixture issuing from the primary induction system, thereby maintaining the volumetric efficiency of the engine at sufficiently high level.
It is known to operate the engine as above with EGR so as to lower NOx emissions. EGR can be effected through the primary induction system that is provided with an induction arrangement to produce a swirl. With the EGR system, because there is a delay in transmission of a change in induction vacuum due to the provision of the swirl producing arrangement a sluggish response to EGR demand will take place during acceleration and because during acceleration a secondary throttle valve of the secondary induction system will open fully before the primary throttle valve of the primary induction system opens fully, an appropriate strength of vacuum will not take place within the primary induction system to draw into the cylinder a quantity of exhaust gas enough to meet the EGR demand for the acceleration.
If EGR is effected through the secondary induction system, the recirculated exhaust gas will not mix well with air fuel mixture drawn from the primary induction system during engine operating condition with low and intermediate loads because under these conditions the recirculated exhaust gas drawn from the secondary induction system and the air fuel mixture from the primary induction system will not meet or mix with each other until they enter a cylinder. As a result, harsh combustion takes place during operation conditions of the engine with low and intermediate loads.